The ultimate goal of our proposed project is the development of an adequate theory of adaptive behaviors shown by persons with mental retardation. Such a theory must deal with the origins and the dimensional structure of behaviors within the domain of adaptive behavior; the theory must deal as well with the growth, maintenance, and aging of adaptive behaviors across the life span and with the factors that moderate the general developmental trends for these behaviors. This study continues our interest in the modeling of development and change in adaptive and maladaptive behaviors across the life span (Eyman & Widaman, 1987; Widaman et al., 1990). In this research two primary questions surface: (a) do different dimensions of adaptive behavior exhibit different age- related trends of growth and development for a given sample of persons, and (b) does each dimension exhibit systematic differences in developmental change for different identifiable groups of people, such as persons differing in level of mental retardation? Longitudinal data on the population of persons with mental retardation receiving services from the State of California (N = 70,000 annually; 45,000 with 7 years of longitudinal data) will be analyzed. Various types of moment and covariance structure models will be fit to the data to characterize patterns of life-span development of adaptive behavior as a function of level of retardation and other relevant personal characteristics and to determine the limits to generalizability of the resulting life span trends.